The Macromolecular Interactions Shared Resource provides Cancer Center researchers with state-of-the art capabilities for the characterization of protein-protein, protein-lipid, protein-nucleic acid and protein-small molecule interactions. The facility provides resources for the complete characterization of macromolecular interactions in solution. This includes a description of the kinetics, thermodynamics and assembly state of the interaction. The strengths of surface plasmon resonance (SPR) include the determination of binding kinetics and equilibria, the determination of active protein concentrations, assay development and drug screening, and binding site and epitope mapping. The strengths of analytical ultracentrifugation (AUG) include the ability to characterize distributions of molecular weight and degree of globularity for macromolecular mixtures simultaneously, and to determine the partial concentration of individual solutes, aiding in the study of conformational changes and sample composition, solution molecular mass, stoichiometry of assembled complexes, and providing rigorous thermodynamics for self-associating systems. Static and dynamic light scattering (LS) are useful tools in the study of the size and size distribution of cells, viruses, micelles, and macromolecules such as proteins, macromolecular assemblies, polysaccharides, and nucleic acids. LS is also useful for the kinetic study of macromolecular assembly and disassembly in real time. By having all of these biophysical tools available in a single shared resource facility, we are able to offer our Cancer Center researchers an extraordinarily high level of rigor and sophistication for the study of the macromolecular complexes and drug targets that have become such an important part of modern cancer research.